Shaker and degasser combination

ABSTRACT

A system for separating components from a slurry of drilling fluid and drill cuttings on a shaker screen having an upper side and a lower side within a shaker. The system also has a pressure differential generator to pull an effective volume of air through a section of the shaker screen to enhance the flow of drilling fluid through the section of the shaker screen and the separation of drilling fluid from drill cuttings and further maintain an effective flow of drill cuttings off the shaker. A method of separating components of a slurry of drilling fluids and solids has the steps of delivering the slurry to a shaker, flowing the slurry over a first screen and applying an effective amount of vacuum to a first portion of the first screen to remove the drilling fluids from the slurry without stalling the solids on the first screen.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority to U.S. patentapplication Ser. No. 13/845,704 which claims benefit to U.S. patentapplication Ser. No. 11/862,955, filed Sep. 27, 2007, which claimsbenefit to U.S. Provisional Patent Application No. 60/827,567, filedSep. 29, 2006, and U.S. Provisional Patent Application No. 60/827,542,filed Sep. 29, 2006. The disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

Embodiments disclosed herein relate generally to shale shakers andscreens for shale shakers. Specifically, embodiments disclosed hereinrelate to a shale shaker having pulse-vacuum assisted screening.Additionally, embodiments disclosed herein relate to methods andapparatus for removing entrained gases from a slurry.

Oilfield drilling fluid, often called “mud,” serves multiple purposes inthe industry. Among its many functions, the drilling mud acts as alubricant to cool rotary drill bits and facilitate faster cutting rates.The mud is mixed at the surface and pumped downhole through a bore ofthe drill string to the drill bit where it exits through various nozzlesand ports, lubricating and cooling the drill bit. After exiting throughthe nozzles, the “spent” fluid returns to the surface through an annulusformed between the drillstring and the drilled wellbore.

Furthermore, drilling mud provides a column of hydrostatic pressure, orhead, to prevent “blowout” of the well being drilled. This hydrostaticpressure offsets formation pressures thereby preventing fluids fromblowing out if pressurized deposits in the formation are breeched. Twofactors contributing to the hydrostatic pressure of the drilling mudcolumn are the height (or depth) of the column (i.e., the verticaldistance from the surface to the bottom of the wellbore) and the density(or its inverse, specific gravity) of the fluid used. Various weightingand lubrication agents are mixed into the drilling mud to obtain theright mixture for the type and construction of the formation to bedrilled. Increasing the amount of weighting agent solute dissolved inthe mud base will generally create a heavier drilling mud. Drilling mudthat is too light may not protect the formation from blowouts, anddrilling mud that is too heavy may over invade the formation. Therefore,much time and consideration is spent to ensure the mud mixture isoptimal. Because the mud evaluation and mixture process is timeconsuming and expensive, drillers and service companies prefer toreclaim the returned drilling mud and recycle it for continued use.

Another significant purpose of the drilling mud is to carry the cuttingsaway from the drill bit to the surface. As a drill bit pulverizes orscrapes the rock formation at the bottom of the borehole, small piecesof solid material are left behind. The drilling fluid exiting thenozzles at the bit stir up and carry the solid particles of rock andformation to the surface within the annulus between the drillstring andthe borehole. Therefore, the fluid exiting the borehole from the annulusis a slurry of formation cuttings in drilling mud, and the cuttingparticulates must be removed before the mud can be recycled.

One type of apparatus used to remove cuttings and other solidparticulates from drilling mud is commonly referred to in the industryas a “shale shaker.” A shale shaker, also known as a vibratoryseparator, is a vibrating sieve-like table upon which returning useddrilling mud is deposited and through which substantially cleanerdrilling mud emerges. Typically, the shale shaker is an angled tablewith a generally perforated filter screen bottom. Returning drilling mudis deposited at the top of the shale shaker. As the drilling mud travelsdown the incline toward the lower end, the fluid falls through theperforations to a reservoir below thereby leaving the solid particulatematerial behind. The combination of the angle of inclination with thevibrating action of the shale shaker table enables the solid particlesleft behind to flow until they fall off the lower end of the shakertable. The above described apparatus is illustrative of one type ofshale shaker known to those of ordinary skill in the art. In alternateshale shakers, the top edge of the shaker may be relatively closer tothe ground than the lower end. In such shale shakers, the angle ofinclination may require the movement of particulates in a generallyupward direction. In still other shale shakers, the table may not beangled, thus the vibrating action of the shaker alone may enableparticle/fluid separation. Regardless, table inclination and/or designvariations of existing shale shakers should not be considered alimitation of the present disclosure.

Preferably, the amount of vibration and the angle of inclination of theshale shaker table are adjustable to accommodate various drilling mudflow rates and particulate percentages in the drilling mud. After thefluid passes through the perforated bottom of the shale shaker, it mayeither return to service in the borehole immediately, be stored formeasurement and evaluation, or pass through an additional piece ofequipment (e.g., a drying shaker, a centrifuge, or a smaller sized shaleshaker) to remove smaller cuttings and/or particulate matter.

Screens used with shale shakers are typically emplaced in a generallyhorizontal fashion on a generally horizontal bed or support within abasket in the shaker. The screens themselves may be flat or nearly flat,corrugated, depressed, or contain raised surfaces. The basket in whichthe screens are mounted may be inclined towards a discharge end of theshale shaker. The shale shaker imparts a rapidly reciprocating motion tothe basket and hence the screens. Material from which particles are tobe separated is poured onto a back end of the vibrating screen, flowingtoward the discharge end of the basket. Large particles that are unableto move through the screen remain on top of the screen and move towardthe discharge end of the basket where they are collected. The smallerparticles and fluid flow through the screen and collect in a bed,receptacle, sump, or pan beneath the screen.

In some shale shakers a fine screen cloth is used with the vibratingscreen. The screen may have two or more overlaying layers of screencloth or mesh. Layers of cloth or mesh may be bonded together and placedover a support, supports, or a perforated or apertured plate. The frameof the vibrating screen is resiliently suspended or mounted upon asupport and is caused to vibrate by a vibrating mechanism (e.g., anunbalanced weight on a rotating shaft connected to the frame). Eachscreen may be vibrated by vibratory equipment to create a flow oftrapped solids on top surfaces of the screen for removal and disposal ofsolids. The fineness or coarseness of the mesh of a screen may varydepending upon mud flow rate and the size of the solids to be removed.

While there are numerous styles and sizes of filter screens, theygenerally follow similar design. Typically, filter screens include aperforated plate base upon which a wire mesh, or other perforated filteroverlay, is positioned. The perforated plate base generally providesstructural support and allows the passage of fluids therethrough, whilethe wire mesh overlay defines the largest solid particle capable ofpassing therethrough. While many perforated plate bases are generallyflat or slightly curved in shape, it should be understood thatperforated plate bases having a plurality of corrugated orpyramid-shaped channels extending thereacross may be used instead. Intheory, the pyramid-shaped channels provide additional surface area forthe fluid-solid separation process to take place, and act to guidesolids along their length toward the end of the shale shaker from wherethey are disposed.

The separation of drilling fluid and other solids from drill cuttingsusing a screen shaker is often incomplete, resulting in wet drillcuttings. As described above, the drilling mud is introduced to the topof the screen and allowed to flow downward through the screen by gravityalone. Often, additional equipment, such as additional screenseparators, hydro cyclones, dryers, drying shakers, centrifuges, hydrocyclone shakers, thermal desorption systems, and other equipment, areused to further dry the cuttings and recover drilling fluid. Forexample, cuttings from a shale shaker may fall onto a rotary vacuumdryer, where the cuttings travel on a circumferentially rotating screen.Air may be used to strip drilling fluid off the cuttings and into thescreen, such as by pulling a vacuum from the interior of the rotatingscreen (for example, the ROTAVAC™ Rotary Vacuum Dryer fluid recovery andcuttings drying system, available from Halliburton).

It is desired to improve the rate and efficiency at which shakers removeliquid from cuttings or other solids. To enhance the gravity-drivenseparation as described above, it is known that increasing the head onthe shaker can increase the throughput of fluids through the screen.Increasing the pressure differential through the screen will likewiseincrease the fluid capacity of the shaker.

One example of a shaker with increased pressure differential isdisclosed by Hensley et al. in U.S. Patent Application Publication No.20050183994A1. Hensley et al. disclose an integrated, transportablecutting treatment system, where a pressure differential is developedacross the screens to increase the flow rate of drilling mud through thescreens. Hensley et al. use an air pump to develop a vacuum beneath thescreens to draw mud through the screens. However, applying a continuousvacuum beneath a screen to draw fluid through the screen may result insolids sticking to the screen, hindering the conveyance of solids offthe end of the shaker as needed, thereby preventing fluids from beingfiltered through the screen.

There exists a continuing desire for shakers having increased fluidcapacity, increased fluid flow-through rates across the screens, and/orimproved fluid removal efficiencies. Accordingly, there exists a needfor a shaker with increased pressure differential. Preferably, the meansused to increase the pressure differential do not substantially hinderthe flow of solids across the screen deck. Additionally, there exists aneed for a shaker for removing entrained gases from the recovereddrilling fluid.

SUMMARY OF THE INVENTION

A system for separating components of a slurry is disclosed, the systemincluding a housing; a basket for holding at least one shaker screen,the basket movably mounted in the housing; at least one vibrator coupledto the basket; a sump disposed below the basket to collect at least aportion of the slurry passing through the at least one shaker screen; apressure differential device fluidly connected to the sump fordeveloping a pressure differential across the at least one shakerscreen; and a toggling device for toggling the pressure differentialacross the screen. In some embodiments, the vapor may be degassed withinthe sump. In other embodiments, the system may include a degassingchamber fluidly connected to the sump and the pressure differentialdevice, wherein the degassing chamber is disposed between the sump andthe pressure differential device; and a fluid conduit fluidly connectedto the degassing chamber for recovering a degassed fluid.

In another aspect, embodiments disclosed herein relate to a method forseparating components of a slurry, the method including providing aslurry to a top of a screen and toggling a pressure differential acrossthe screen from static to a vacuum below the screen. In someembodiments, the toggling may include generating at least a partialvacuum below the screen by causing a flow of vapor from a vapor spacebelow the screen, and intermittently interrupting the vacuum bydisrupting the flow of vapor. In other embodiments, the partial vacuummay be generated by causing a flow of fluid from a space below thescreen, the fluid may be degassed to recover a vapor and a degassedliquid, and the toggling may be performed by intermittently interruptingthe vacuum by disrupting the flow of recovered vapor.

In an aspect of the invention, a method of separating components of aslurry of drilling fluids and solids is provided. The method has thesteps of delivering the slurry to a shaker; flowing the slurry over afirst screen; and applying an effective amount of vacuum to a firstportion of the first screen to remove the drilling fluids from theslurry without stalling the solids on the first screen.

In an embodiment, the method has the step of intermittently interruptingand/or pulsing the amount of vacuum applied to the first screen.

In an embodiment, the method has the step of controlling the air flowunder the screen to prevent stalling of drill cuttings in the slurry onthe screen.

In an embodiment, the method has a step of applying a vacuum force tothe shaker screen sufficient to effectively reduce drilling fluidretained on cuttings in the slurry to a level below that obtained whenno vacuum force is applied.

In another aspect of the invention, a system for separating componentsfrom a slurry of drilling fluid and drill cuttings on a shaker isprovided. The system has a shaker screen having an upper side and alower side for separating drill cuttings and drilling fluid within ashaker. The system also has a pressure differential generator to pull aneffective volume of air through a section of the shaker screen toenhance the flow of drilling fluid through the section of the shakerscreen and the separation of drilling fluid from drill cuttings andfurther maintain an effective flow of drill cuttings off the shaker.

In an embodiment, the system has a toggling device to alternate apressure differential below the section of the shaker screen from zerovacuum to at least a partial vacuum.

In an embodiment, the effective volume of air pulled through the screenis adjustable to prevent stalling of drill cuttings in the slurry on thescreen. In another embodiment, the system has a plurality of shakerscreens wherein the pressure differential generator pulls an effectivevolume of air through a section of the screens.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of a vibratory screen separator useful inembodiments disclosed herein.

FIG. 2 is a cross-sectional view of the screen separator of FIG. 1.

FIG. 3 is a side view of a vibratory screen separator useful inembodiments disclosed herein, where the separator may be fluidlyattached to a vacuum system.

FIG. 4 is a perspective view of a vibratory screen separator frame andsump useful in embodiments disclosed herein.

FIG. 5 is a simplified flow diagram for embodiments of a system forgenerating a pressure differential across a screen and degassing a fluidaccording to embodiments disclosed herein.

FIG. 6 is a simplified flow diagram for embodiments of a system forgenerating a pressure differential across a screen and degassing a fluidaccording to embodiments disclosed herein.

FIG. 7 is a perspective view of a vibratory screen separator having avacuum fume extraction device in accordance with embodiments disclosedherein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one aspect, embodiments disclosed herein relate to a method forseparating components of a slurry. As used herein, a slurry refers to amixture of drilling fluid and drill cuttings. A slurry may be separatedusing a screen separator having a pressure differential across thescreen. In other aspects, embodiments disclosed herein relate to asystem for separating components of a slurry. The system may include, insome embodiments, a vibratory screen separator and a pressuredifferential device or a vacuum generating device. The pressuredifferential device may additionally provide a driving force to degasthe recovered drilling fluid.

FIGS. 1 and 2 illustrate one embodiment of a vibratory screen separator.The separator 5 includes a base 10 having four legs 12 and supportingmembers 14. Mounted on the four legs 12 are resilient mounts 16. Eachmount 16 includes a spring 18, a base 20 on each leg and a socket 22 onthe separator to receive each spring 18. Positioned on the base 10 bythe resilient mounts 16 is a separator frame or basket 24. The basket24, includes sidewalls 26 and 28 and a back wall 30. The front side,opposite to the back wall 30, may be left open. The basket 24 is ofsufficient structure to withstand the vibrational loads imposed on thebasket 24 in operation. Extending across the interior of the basket 24between the sidewalls 26 and 28 is a structural tube 32 which may bepositioned at roughly the center of mass for further structuralstrength.

Located about the sidewalls 26 and 28 and the back wall 30 is a channel34. Located above the channel 34 on the sidewalls 26 and 28 are stops 38and 40. The stops cooperate with the channel 34 through its extent alongthe sidewalls 26 and 28 to form a screen mounting in a first plane. Ascreen 42 having a screen frame 44 and screen cloth 46 is illustratedpositioned in the screen mounting. Resilient members 48 are positionedon the underside of the stops 38 and 40 to help locate, seat and sealthe screen frame 44. Obviously, multiple screens 42 may be employed inanyone separator.

A sump 50 is located below the screen mounting to receive materialpassed through the screen 42. An inlet 52 is positioned at the back wall30 above the screen mounting. An outlet 54 for material passed throughthe screen 42 receives material from the sump 50 for discharge. Materialnot passing through the screen 42 is discharged off the end of thescreen 42 and suitably collected. The flow across the screen plane fromthe inlet 52 toward the outlet 54 defines a linear direction of materialtravel. Attached to the sides of the basket 24 and specifically to eachsidewall 26 and 28 are two rotary eccentric vibrators 56 and 58.

As illustrated in FIGS. 1 and 2, sump 50 may be integrally connected tobasket 24. Thus, sump 50 may be referred to as a vibrating sump. Inother embodiments, sump 50 may be separate from basket 24, a stationarysump.

A pressure differential device (not shown) may be provided to create apressure differential between the vapor space above screen and the vaporspace between screen 42 and sump 50. In some embodiments, the pressuredifferential device may be located internal to sump 50, such as an airpump (not shown). In other embodiments, the pressure differential devicemay be located external to sump 50, such as a vacuum system (not shown).Whether internal or external to sump 50, the pressure differentialdevice may cause vapor to flow from the vapor space between screen 42and sump 50 to a point external to sump 50, such as through outlet 54 orother conduits forming an outlet from sump 50.

The pressure differential device may include, in some embodiments,pumps, blowers, aspirators, ejectors, and the like, and combinationsthereof. In various embodiments, the pressure differential may becreated by one or more of a positive displacement pump, a momentumtransfer pump, or an entrapment pump.

Pumps useful in creating the pressure differential or vacuum m someembodiments include reciprocating pumps, centrifugal pumps, vacuumpumps, pneumatic pumps, electric pumps, air pumps, piston pumps, rotarypiston pumps, rotary vane pumps, screw pumps, scroll pumps, liquid ringpumps, external vane pumps, Wankel pumps, Toepler pumps, and Venturivacuum pumps, among others. Blowers useful in creating the pressuredifferential may include booster pumps, a rotary lobe blower (such as aROOTS™ blower), and vacuum blowers. Useful ejectors and aspirators mayinclude steam ejectors, water aspirators, or ejectors and aspiratorsutilizing other motive fluids. In some embodiments, drilling fluid isused as the motive fluid for an ejector or an aspirator.

In some embodiments, the pressure differential may be pulsed, toggled,or intermittently interrupted. Toggling or pulsing of the pressuredifferential, as used herein, refers to the changing of the pressuredifferential from static (a zero pressure differential across thescreen) to at least a partial vacuum below the screen. In someembodiments, the pressure differential may be toggled from static to atleast a partial vacuum. In other embodiments, the pressure differentialacross a screen may be toggled or pulsed from static to a full vacuumbelow the screen. In some embodiments, the pressure differential may betoggled from static to a pressure differential in the range from about−0.1 to about −1.0 bar, as given by a quantity defined as a pressurebelow the screen minus a pressure above the screen. In otherembodiments, the pressure differential may be toggled from static to apressure differential in the range from about −0.2 to about −0.7 bar, asgiven by a quantity defined as a pressure below the screen minus apressure above the screen; from static to a pressure differential in therange from about −0.2 to about −0.7 bar in other embodiments; and fromabout −0.3 bar to about −0.6 bar in yet other embodiments. By togglingthe pressure between vacuum and static, conveyance of solids across thescreen may proceed unhindered, thereby avoiding solids accumulating orsticking on the screen, and thus not preventing fluid flow through thescreen.

Pulsing or toggling the pressure differential between static and vacuumbelow the screen, in some embodiments, may be effectuated by a valvedisposed between the pressure differential device (pumps, ejectors,etc., as described above) and the screen. Manipulating the valve byopening and/or closing the valve, at least partially, may disrupt theflow of vapor from the sump, thereby affecting the pressuredifferential. In other embodiments, the toggling device, such as avalve, may be disposed between a vacuum generating device or system andthe sump located under one or more of the screens.

Valves useful for toggling the pressure differential may include rotaryvalves, ball valves, globe valves, needle valves, butterfly valves, gatevalves, plug valves, diaphragm valves, and piston valves, among others.The valves may be manually operated in some embodiments, or may beremotely actuated valves in other embodiments.

In some embodiments of the pulsed-vacuum assisted screening devicedisclosed herein, the separator may include two or more screens. One ormore sumps may be located under the screens such that a pressuredifferential may be provided across less than all of the two or moreshaker screens. In other embodiments, the same or different pressuredifferentials may be provided across zoned shaker screens.

FIG. 3 illustrates one embodiment of a pulsed-vacuum assisted screeningdevice having separate pressure zones, where like numerals representlike parts. Separator 60 may include two or more screens (not shown),correspondingly located above two or more sumps 50 (i.e., 50A and 50B asillustrated). For example, where separator 60 has four screens inseries, sump 50A may be located proximate inlet 52 under the first twoscreens. Sump 50B may be located proximate outlet 54B, under the lasttwo screens (where first and last corresponds to the direction of flowfrom inlet 52 to outlet 54B). Sump 50A may thus create an independentzone from sump 50B, allowing for operations of the two zones at the sameor different pressure differentials. One or more devices may be providedto create a pressure differential across either or both sets of screens.The pressure differential across the screens in either zone may bemanipulated to provide additional capacity or to enhance the liquidrecovery, resulting in a dryer cutting fraction. To maintain separatepressure differentials, sumps 50A and 50B may not be in fluidcommunication. As such, outlet 54A may be provided to discharge materialpassing through the first two screens into sump 50A.

As described above, one or more pressure differential devices may beprovided to create a pressure differential between the vapor space abovethe screens and the vapor space between the screens and sumps 50A, 50B.In some embodiments, the pressure differential devices may be locatedinternal to sumps 50A, 50B. In other embodiments, the pressuredifferential devices may be located external to sumps 50A, 50B. Whetherinternal or external to sumps 50A, 50B, the pressure differentialdevices may cause vapor to flow from the vapor space between the screenand sump 50A, 50B to a point external to each sump 50A, 50B, such asthrough outlets 54A, 54B, or other conduits forming an outlet from sumps50A, 50B.

For example, outlet 54A may be used as a liquid outlet, discharging thedrilling fluid and other solids passing through screens. An outlet 56Amay be provided to convey vapor from sump 50A to create the desiredpressure differential. Outlet 56A, in some embodiments, may be connectedto a lobe pump 58 or to one or more vacuum generating devices asdescribed above. The vapor discharge from vacuum generating device 58may then be vented or further processed, such as through a vaporrecovery or incineration system 59.

FIG. 4 illustrates another embodiment of the pulsed-vacuum assistedscreening device. The separator may include a base, legs, supportingmembers, and other component parts as previously illustrated formounting separator frame 74. Separator frame 74 may include sidewalls76, 78 and a back wall 80. The front side 81, opposite to the back wall80, may be left open. The frame 74 may be of sufficient structure towithstand the vibrational loads imposed on the frame 74. Extendingacross the interior of the frame 74 between the sidewalls 76, 78 may bea structural tube 82 which may be positioned at roughly the center ofmass, for further structural strength.

Located about the sidewalls 76 and 78 and the back wall 80 is a channel(not shown). Located above the channel on the sidewalls 76 and 78 arestops 88 and 90. The stops cooperate with the channel (not shown)through its extent along the sidewalls 76 and 78 to form a screenmounting in a first plane. A screen 92 is illustrated positioned in thescreen mounting. Multiple screens 92 may be employed in anyoneseparator.

One or more shaker screens 92 may be installed in, or secured to, theshale shaker frame 74 with a wedge block 94. The screen 92 is placed ona support rail (not shown) and positioned underneath a stationary wedgeguide 88 (stop 88). The wedge block 90 (stop 90) is then pounded intoposition so as to secure the screens 92 to frame 74. One of ordinaryskill in the art will appreciate that the operator often chooses to usea combination of a hammer and a suitable piece of wood in contact withthe wedge block 90 to deliver sufficient force to fully tighten thewedge block 90. As shown in FIG. 4, the wedge block 90 may also includea hammer surface 94 to aid in installation (as by pounding on surface 94a) and removal (as by pounding on surface 94 b).

An inlet (not shown) may be located proximate back wall 80. The solidsmay then travel on top of the screens toward front side 81. Asillustrated, the separator has four screens 92. The drilling mud may bedeposited on the first screen 92A. A sump 96 may be provided under thefirst two screens 92A, 92B. As illustrated, sump 96 may be integrallyformed with frame 74. One or more pressure differential devices, asdescribed above, may be provided to generate a pressure differentialacross screens 92A, 92B. An outlet 98 may be provided to convey vaporfrom sump 96 to create the desired pressure differential.

Referring now to FIG. 5, a simplified flow diagram for embodiments of asystem for generating a pressure differential across a screen anddegassing a fluid, according to embodiments disclosed herein, isillustrated. A shaker 100 may include a basket 102, shaker screen 104,and sump 106, as described above. A drilling fluid 108 to be separated,such as a mixture of drilling mud and drill cuttings, may be fed toinlet end A of the shaker 100. Drill cuttings separated from drillingfluid 108 may be recovered at outlet end B. The drilling mud 110separated from the drill cuttings may be collected in sump 106.

To generate the desired intermittent pressure differential across screen104, the vapor space 112 of sump 106 may be fluidly connected via flowline 113 to a valve 114 and a pressure differential device 116, asdescribed above. To prevent liquids from entering flow line 113 andpressure differential device 116, vacuum system inlet 118 may bedisposed vertically downward, may include a cover 120, such as to directfluid away from inlet 118, or may include other safety devices toprevent fluid from entering the vapor system.

Vapors recovered via pressure differential device 116 may be flared,vented, or recovered via flow line 122. Fluids 110 may be recovered fromsump 106 via flow line 124, and in some embodiments may be directed to amud tank for further processing and/or recycled to the mud system.

In the embodiment illustrated in FIG. 5, the fluid 110 collecting insump 106 during the separations may be degassed or partially degassed bythe vacuum or partial vacuum generated by pressure differential device116. Operation of pressure differential device 116 results in at least apartial vacuum in sump 106, and may provide a driving force for gasesthat may be dissolved or entrained in the fluid 110 to be separatedtherefrom.

If necessary, a vent 126 may be provided to aid in pressure control ofsump 106 or to provide means to avoid under-pressure of sump 106, wherevent 126 may include pressure relief valves and other devices known inthe art to provide flow in limited circumstances.

Referring now to FIG. 6, a simplified flow diagram for embodiments of asystem for generating a pressure differential across a screen anddegassing the recovered fluid, according to embodiments disclosedherein, is illustrated. A shaker 200 may include a basket 202, shakerscreen 204, and sump 206, as described above. A drilling fluid 208 to beseparated, such as a mixture of drilling mud and drill cuttings, may befed to inlet end A of the shaker 200. Drill cuttings separated fromdrilling fluid 208 may be recovered at outlet end B. The drilling mud210 separated from the drill cuttings may be collected in sump 206.

To generate the desired intermittent pressure differential across screen204, sump 206 may be fluidly connected via flow line 213 to a degassingchamber 212, valve 214, and a pressure differential device 216, asdescribed above. Generation of the intermittent pressure differentialacross screen 204 results in both liquids and vapors being pulled fromsump 206 to degassing chamber 212. The vapors collecting in degassingchamber 212 may be recovered via flow line 217, and may be flared,vented, or otherwise recovered via flow line 222. Fluids 210 collectingin degassing chamber 212 may be recovered via flow line 224, and in someembodiments may be directed to a mud tank for further processing and/orrecycling to the mud system. If necessary, a vent 226 may be provided toaid in pressure control of degassing chamber 212, where vent 226 mayinclude pressure relief valves and other devices known in the art toprovide flow in limited circumstances.

The fluid 210 collecting in degassing chamber 212 during the separationprocess may be degassed or partially degassed by the vacuum or partialvacuum generated by the pressure differential device 216. Operation ofpressure differential device 216 results in at least a partial vacuum indegassing chamber 212, and may provide a driving force for gases thatmay be dissolved or entrained to be separated from the fluid 210. Suchdegassing that may occur in embodiments described herein may allow for asimplified mud tank system, where vents and other degassing equipmentmay not be necessary.

As described above, shaker systems described herein may include apressure differential device or vacuum generating device to generate anintermittent pressure differential across a shaker screen. The vacuumgenerated by the pressure differential device may provide an additionaldriving force for separating fluids from drill cuttings, and mayadditionally remove vapors and entrained gases from the filtereddrilling fluid.

Referring now to FIG. 7, a perspective view of a vibratory separator 500in accordance with an embodiment of the present disclosure is shown. Inthis embodiment, vibratory separator 500 includes a housing 502, adrilling fluid inlet end 504, an outlet end 506, and a plurality shakerscreens 508. In the embodiment shown, the plurality of shaker screens508 are assembled in a multi-tier configuration. By vertically stackingmultiple shaker screens 508, the footprint of vibratory separator 500 isdecreased, thereby providing equivalent separating potential whilerequiring less space. In vibratory separators 500 using verticallystacked shaker screens 508, the size of the apertures in the screens maybe varied according to each tier. As drilling fluid begins to flow froma top tier of vibratory separator 500, the screen assembly apertures maybe substantially greater in size than the apertures of lower screenassemblies. To prevent drilling fluid from falling on lower disposedshaker screens assemblies 508, a series of flowback pans 522 may belocated under shaker screens 508. Flowback pans 522 may be directed todeposit drilling fluid into a sump 510, thereby allowing drilling fluidto be substantially cleaner at each level of processing.

In this embodiment, vibratory separator 500 also includes a fumehood/outlet 516 connected to housing 502. In one embodiment, the fumehood/outlet 516 may include a vacuum system that extracts vapors intothe vent hood/outlet 516. As drilling fluid enters vibratory shaker 500through inlet end 504, the drilling fluid falls onto shaker screen 508and is conveyed from inlet end 504 to outlet end 506 using vibratorymotion and pulse-assisted screening devices as described above. As thedrilling fluid is conveyed, vapors, including potentially hazardousgases, for example, hydrogen sulfide (“H₂S”), entrained in the drillingfluid may be present.

In this embodiment, fume hood/outlet 516 is configured to extract vaporsfrom the drilling fluid as it flows across the shaker screens 508. Asvapors and fumes are released in a generally upward direction from thedrilling fluid, fume hood/outlet 516 may pull the vapors and fumesinward, thereby trapping the potentially hazardous fumes and/or vapors.Those having ordinary skill in the art will appreciate that by using afume hood, potentially noxious odors/hazardous conditions may be avoidedby directing the flow of air into the hood. Once directed into the hood,a number of subsequent steps may be performed to further treat or ventthe trapped gases.

One of ordinary skill in the art will appreciate that fume hood/outlet516 may be turned on during any step of the separation process includingduring normal separation, during cleaning, or substantiallycontinuously. Thus, embodiments including fume hood/outlets 516 mayprovide for a vibratory separator 500 that is substantially enclosed,thereby preventing the escape of hazardous materials and/or vapors intothe drilling work space.

In one embodiment, vibratory separator 500 may further include one ormore pressure differential devices (not shown) to create a pressuredifferential between a vapor space 512 above and between the screens 508and sump 510. In some embodiments, the pressure differential devices(not shown) may be located internal to sump 510. In other embodiments,the pressure differential devices (not shown) may be located external tosump 510. Whether internal or external to sump 510, the pressuredifferential devices (not shown) may cause vapor to flow from the vaporspace between the screens 508 and sump 510 to a point external to sump510, such as through outlets 54A, 54B (shown in FIG. 3). Fumehood/outlet 516 may be in fluid connection with outlets 54A, 54B to pullvapors that flow through such outlets 54A, 54B, thereby trapping thepotentially hazardous fumes and/or vapors. Vapors and fumes trapped infume hood/outlet 516 may be treated and/or safely removed from vibratoryshaker 500 thereafter.

In other embodiments, vibratory separator 500 may include one or morepressure differential devices (not shown) to create a pressuredifferential between a vapor space 512 above the screens 508 andflowback pans 522. In some embodiments, the pressure differentialdevices (not shown) may be located internal to flowback pans 522. Inother embodiments, the pressure differential devices (not shown) may belocated external to flowback pans 522. Whether internal or external toflowback pans 522, the pressure differential devices (not shown) maycause vapor to flow from the vapor space between the screens 508 andflowback pans 522 to a point external to flowback pans 522, such asthrough outlets 54A, 54B (shown in FIG. 3). Fume hood/outlet 516 may bein fluid connection with outlets 54A, 54B to pull vapors that flowthrough such outlets 54A, 54B, thereby trapping the potentiallyhazardous fumes and/or vapors. Vapors and fumes trapped in fumehood/outlet 516 may be treated and/or safely removed from vibratoryshaker 500 thereafter.

In one embodiment, after the drilling fluid passes through shakerscreens 508, the drilling fluid may be directed to a containment areawhere the drilling fluid may be degassed to remove remaining entrainedgases. Degassing the drilling fluid may be performed by any method knownin the art. For example, mechanical degassers and aeration devices mayused, as disclosed in U.S. Pat. Nos. 7,727,316 and 7,704,299, assignedto the assignee of the present application, and incorporated herein byreference in their entireties. A mechanical degasser may exert acentrifugal force on the drilling fluid. The centrifugal force of themechanical degasser multiplies the force acting on the entrained gas(e.g., H₂S) to increase buoyancy of the gas, thereby releasing entrainedgas from the drilling fluid. The increase in buoyancy of the gasaccelerates the bubble-rise velocity of the gas velocity, and as the gasbubbles rise toward the surface, they escape the drilling fluid. One ofordinary skill in the art will appreciate that any device known in theart that exerts a centrifugal force on the fluid, thereby reducing theamount of entrained or dissolved gases in the process fluid, may be usedin place of a mechanical degasser.

Advantageously, embodiments disclosed herein may provide shakers havingincreased fluid capacity, increased fluid flow-through rates across thescreens, and/or improved fluid removal efficiencies. Also,advantageously, embodiments disclosed herein may provide shakers withreduced hazardous vapors in vapor spaces. Finally, embodiments disclosedherein may provide shakers that more efficiently separate entrainedgases from drilling fluids.

While the present disclosure has been described with respect to alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that other embodiments can bedevised which do not depart from the scope of the disclosure asdescribed herein. Accordingly, the scope of the present disclosureshould be limited only by the attached claims.

I claim:
 1. A method comprising: introducing a slurry to a shaker havinga first screen and a second screen; flowing the slurry over the firstscreen; applying a first pressure differential with a pressuredifferential device to at least a portion of the first screen toseparate a solids component from a liquid component of the slurry; andpulling the liquid component and air or vapor together through a flowline in fluid communication with the pressure differential device into adegassing chamber while maintaining the first pressure differentialacross the first screen.
 2. The method of claim 1 further comprising:applying a second pressure differential to the second screen wherein thesecond pressure differential is less than the first pressuredifferential.
 3. The method of claim 1 further comprising: applying asecond pressure differential to the first screen wherein the secondpressure differential is zero.
 4. The method of claim 1 furthercomprising: toggling the first pressure differential between static andat least a partial vacuum.
 5. The method of claim 1 further comprising:intermittently interrupting the step of applying the first pressuredifferential.
 6. The method of claim 1 further comprising: pulsing thestep of applying the first pressure differential between the firstpressure differential and a second pressure differential wherein thesecond pressure differential is different than the first pressuredifferential.
 7. The method of claim 1 further comprising: applying athird pressure differential to a second portion of the first screen. 8.The method of claim 1 wherein the applying the first pressuredifferential is generated by a vacuum external to the shaker.
 9. Themethod of claim 1 further comprising: controlling air flow under thescreen to prevent stalling of the slurry on the screen.
 10. A methodcomprising: delivering a slurry to a shaker to flow over a first screenand a second screen of the shaker, the slurry having a drilling fluidcomponent and a solids component; generating a first pressuredifferential between an area above a portion of the first screen and anarea below the portion of the first screen inside the shaker, whereinthe pressure differential is created by a device external to the shaker;and pulling air or vapor and substantially all of the drilling fluidcomponent together from the area below the first screen inside theshaker into a degassing chamber external to the shaker while maintainingthe first pressure differential.
 11. The method of claim 10 furthercomprising: intermittently interrupting the first pressure differentialapplied to the first screen.
 12. The method of claim 10 furthercomprising: pulsing the first pressure differential applied to the firstscreen.
 13. The method of claim 10 further comprising: applying thefirst pressure differential to a first portion of a second screen. 14.The method of claim 10 further comprising: separating the air or vaporfrom the drilling fluid component in the degassing chamber.
 15. Themethod of claim 10 further comprising: applying vacuum pressure to aportion of the total length of the first screen.
 16. A systemcomprising: a first screen having an upper side and a lower side forseparating drill cuttings and drilling fluid within a shaker; a pressuredifferential generator configured to pull air or vapor through at leasta portion of the first screen to enhance a flow of drilling fluidthrough the first screen with respect to a second screen within theshaker in which the pressure differential generator does not create apressure differential between an area above and an area below the secondscreen; a sump disposed below the first screen and configured to receivethe flow of drilling fluid through the first screen; and a chamber influid communication with the pressure differential generator and locatedexternal to the shaker for collecting the air or vapor and the drillingfluid from the sump while the pressure differential generator isconfigured to apply a pressure differential across the first screen. 17.The system of claim 16 wherein the pressure differential generator islocated external to the shaker.
 18. The system of claim 16 wherein theair or vapor pulled through the first screen is adjustable to preventstalling of drill cuttings on the first screen.
 19. The system of claim16 further comprising: a second pressure differential generatorconnected to a third screen within the shaker for generating a secondpressure differential across the third screen wherein the secondpressure differential is different than the pressure differential of thefirst screen.